The present invention relates to a socket for a wedge base bulb used as a lamp for a motor vehicle, etc., which eliminates not only looseness of the bulb fitted into the socket but at the time of improper insertion of the bulb into the socket, deformation of a terminal mounted in the socket.
In a known socket for a wedge base bulb 6 as shown in FIGS. 1 and 2, a substantially I-shaped opening 2 for receiving the bulb 6 is formed in a cylindrical socket body 1 and terminals 3A and 3B each having a pair of contact pieces 4 are symmetrically fitted into the opening 2 so as to interpose a central bore 5 therebetween such that the contact pieces 4 of the terminal 3A confront the contact pieces 4 of the terminal 3B, respectively. Furthermore, in the socket body 1, ribs 13A to 13F project radially inwardly from an inner face of a circumferential wall 12 into the opening 2 and are spaced circumferentially from each other. Radially inner faces of the ribs 13A to 13F are so formed as to define a circle.
As shown in FIG. 3, the bulb 6 has a glass globe 7, a pair of base portions 8 provided at a bottom of the glass globe 7 and a cylindrical stem 9 extending between the base portions 8. Each of the base portions 8 is formed with a recess 8a such that lead wires 10A and 10B project from the recesses 8a, respectively. When the bulb 6 is fitted into the known socket, not only each of the base portions 8 is positioned between the contact pieces 4 of each of the terminals 3A and 3B mounted in the socket body 1 but the stem 9 is positioned at the central bore 5 such that the bulb 6 is inserted into the opening 2. Then, each of the base portions 8 is gripped between the contact pieces 4 of each of the terminals 3A and 3B such that the bulb 6 is clamped. As a result, each of the lead wires 10A and 10B is brought into contact with one of the contact pieces 4 of each of the terminals 3A and 3B.
Meanwhile, a hole 12 for receiving a connector (not shown) is formed at one end of the terminal body 1 remote from the opening 2. As shown in FIG. 2, a connector contact 12 extends downwardly from the contact pieces 4 of each of the terminals 3A and 3B and protrudes into the hole 12 so as to be connected to the connector fitted into the hole 12.
In the bulbs of this kind, an outside diameter D1 (FIG. 3(a)) of the glass globe 7 is stipulated by the Japanese Industrial Standards (JIS) so as not to exceed 10.29 mm. However, a minimum value of the outside diameter D1 of the glass globe 7 has not been stipulated by JIS. The glass globe 7 of 9.60 to 10.20 mm in outside diameter is usually used. However, diameter of the opening 2 for receiving the bulb 6 should be set such that the bulb 6 having the glass globe 7 of 10.29 mm in outside diameter can be inserted into the opening 2. Therefore, as shown by the broken lines in FIGS. 1 and 2, diameter of the opening 2 is set on the basis of the maximum value of 10.29 mm in the outside diameter D1. Namely, it is so arranged that the radially inner faces of the ribs 13A to 13F are brought into contact with the outer peripheral surface of the glass globe 7 having the maximum value of 10.29 mm in the outside diameter D1 so as to hold the glass globe 7.
Therefore, in case the glass globe 7 of the bulb 6 to be fitted into the opening 2 has the maximum value of 10.29 mm in the outside diameter D1, the glass globe 7 is brought into contact with the radially inner faces of the ribs 13A to 13F of the socket body 1 without any clearance therebetween, so that the glass globe 7 is not set loose in the opening 2 even when vibrations are applied to the motor vehicle.
However, in case the outside diameter D1 of the glass globe 7 of the bulb 6 is less than the maximum value of 10.29 mm, for example, the outside diameter D1 of the glass globe 7 is 9.60 mm, a clearance G of about 0.35 mm is formed between the glass globe 7 and each of the radially inner faces of the ribs 13A to 13F as shown in FIG. 4. Therefore, if vibrations in the direction of the arrow shown in FIG. 5 are applied to the known socket, the glass globe 7 is set loose in the socket body 1 due to the clearance G, thereby resulting in detachment of the bulb 6 from the socket body 1 or deterioration of reliability of electrical contact between the lead wires 10A and 10B of the bulb 6 and the terminals 3A and 3B.
As shown in FIG. 6, a pair of parallel walls 15 confront each other in the opening 2 so as to support the contact pieces 4 of each of the terminals 3A and 3B such that an upper end 4a of each of the contact pieces 4 of each of the terminals 3A and 3B extends above an upper end 15a of each of the parallel walls 15. Therefore, if the bulb 6 is improperly inserted into the opening 2, for example, obliquely as shown by the arrow Al or at a location far distant from the axis of the opening 2 as shown by the arrow A2 when the bulb 6 is fitted into the socket body 1, such an undesirable phenomenon may take place that the base portions 8 of the bulb 6 interfere with or depress the upper end 4a of one of the contact pieces 4 so as to deform the contact piece 4 as shown by the two-dot chain lines in FIG. 6. Once the contact piece 4 has been deformed due to improper insertion of the bulb 6 into the opening 2 of the socket body 1, the bulb 6 cannot be fitted into the socket body 1 smoothly even if the bulb 6 is properly inserted into the opening 2 subsequently.